Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$172.94	10.543%	$191.1731	$191.17	$191.15	$191.20
Purchase #2	$218.65	6.588%	$233.0547	$233.05	$233.05	$233.10
Purchase #3	$46.59	12.352%	$52.3448	$52.34	$52.35	$52.30
Purchase #4	$92.53	9.640%	$101.4499	$101.45	$101.45	$101.40
Purchase #5	$27.63	6.402%	$29.3989	$29.40	$29.40	$29.40
Purchase #6	$85.82	6.487%	$91.3871	$91.39	$91.40	$91.40
Purchase #7	$140.64	8.331%	$152.3567	$152.36	$152.35	$152.40
7 purchase totals =	$784.80		$851.1652	$851.16	$851.15	$851.20